1. Field of the Invention
The present invention relates to refrigeration systems and more particularly to refrigeration systems having refrigerant flow reversing valves.
Flow reversing valves are commonly used in refrigeration systems employing a refrigerant compressor, a refrigerant condensing heat exchanger and a refrigerant evaporating heat exchanger. In a typical system gaseous refrigerant is compressed by the compressor and discharged to a refrigerant condensing heat exchanger in the form of a relatively high temperature, high pressure gas. Heat is transferred from the gas in the condensing heat exchanger to the ambient atmosphere causing the refrigerant to condense and pass from the heat exchanger in liquid form at relatively high pressure. Condensation of the refrigerant results in heating the ambient atmosphere by the condensing heat exchanger.
The liquid refrigerant next passes through an expansion device formed by a flow restriction and evaporates at a relatively lower pressure in the refrigerant evaporating heat exchanger. The heat required for evaporating the refrigerant is transferred to it from the atmosphere surrounding the evaporating heat exchanger thus effectively chilling the atmosphere. Refrigerant passing from the evaporating heat exchanger flows to the compressor inlet where the refrigeration cycle is begun again.
Where a refrigeration system is used as a so-called heat pump, the direction of flow of the refrigerant is reversible so that a single heat exchanger serves to evaporate refrigerant and cool air in an air conditioned space during hot weather and to condense refrigerant and heat air in the space during cold weather.
The refrigerant flow is reversed by operation of a refrigerant flow reversing valve. Typical flow reversing valves have a first port communicating with the compressor discharge, a second port communicating with the compressor inlet and third and fourth ports communicating with the respective heat exchangers. The flow reversing valve contains a valve member which communicates refrigerant discharged from the compressor to one of the heat exchangers while communicating the outlet of the other heat exchanger to the compressor inlet. The valve member is actuated to reverse the direction of refrigerant flow through the heat exchangers.
Refrigerant flow reversing valves are also used in refrigeration systems for reversing the flow of refrigerant for relatively brief periods of time in order to direct hot refrigerant gas into the refrigerant evaporating heat exchangers in order to defrost the evaporating heat exchangers.
2. The Prior Art
Numerous refrigerant flow reversing valve configurations have been proposed by the prior art. Many of the proposed valves have not been commercially acceptable because of failure to meet performance criteria necessary for use in refrigeration systems. Refrigerant flow reversing valves must be capable of operating with relative ease under substantial differential pressures (i.e., the reversing valve member is constantly subjected to the differential pressure existing between the compressor inlet and discharge). Moreover, the valve member is constantly subjected to significant temperature gradients (i.e., the difference in temperature between the refrigerant exiting the evaporating heat exchanger and the refrigerant being delivered to the condensing heat exchanger). In addition, the valve member must permit no more than a minimal amount of leakage of the high pressure refrigerant to the compressor inlet to maximize the system operating efficiency, and the valve member must operate between its alternative positions quickly and reliably throughout a large number of cycles of operation.
One configuration of refrigerant flow reversing valve which has proved notably successful is disclosed by U.S. Pat. No. 3,056,574. This valve employs a generally cylindrical valve housing defining a chamber with a first port in one side communicating with the compressor discharge. A bearing surface is disposed in the chamber opposite the first port and second, third and fourth ports open in the chamber through the bearing surface. The second port communicates with the compressor intake and is located between the third and fourth ports.
A flow reversing valve member is slidably supported on the bearing surface for alternatively communicating the second port with the third port or the fourth port. When the second and third ports are in communication the first and fourth ports communicate so that refrigerant from the compressor discharge flows through the valve chamber via the first and fourth ports. When the second and fourth ports are communicated by the valve member the refrigerant from the compressor discharge flows through the valve chamber via the first and third ports.
The valve member is formed by a body defining a cavity through which the second and third or fourth ports are communicated. A valve body surface surrounding the cavity sealingly engages the bearing surfaces and slides on the bearing surface when the valve member changes position. The valve body is connected to an actuator for changing the valve position.
The valve member is urged with significant force against the bearing surface and when the valve member slides across the ports in the bearing surface the valve body surface tends to be subjected to impacts as the bearing crosses the edges of the ports as well as to abrasive wearing, resulting in refrigerant leakage and reduction of valve life. Consequently the valve body and bearing surface were constructed from metal, such as brass, and lapped to assure smooth and intimate face contact between them.
Attempts were made to reduce the cost of refrigerant reversing valves by forming the valve body of a rigid relatively low friction plastic material. A valve constructed in this manner is disclosed by U.S. Pat. No. 2,976,701. Valve bodies constructed from fiber reinforced nylon had requisite strength, but exhibited undue wearing of the valve body faces. Valve bodies constructed from polytetrafluoroethylene (for example, a material sold under the trademark Teflon) exhibited satisfactory wear and friction characteristics but were not structurally capable of use in the environment because of the temperature and pressures encountered.
A valve body constructed from drawn metal cups supporting a polytetrafluoroethylene valve body face is disclosed by U.S. Pat. No. 3,032,312. This construction has proved quite successful in that the drawn metal ciups are rigid and structurally strong and form a smoothly contoured cavity for directing refrigerant flow. The polytetrafluoroethylene valve body face is formed by an endless band of material which is grasped and supported by the valve body cups. The face thus provides low friction sliding engagement between the valve body and the bearing surface without structurally weakening the valve body.
While this valve body construction has been successfully used in refrigerant flow reversing applications, constructing and assembling its components has created undesirably high production costs.